Ankle-foot orthosis are used to control the alignment and motions of the joints of the foot and ankle of a patient. In a conventional arrangement, the AFO is constructed of metal and plastic usually consisting of two metal uprights or posts whose proximal ends are connected to a leather-covered metal or plastic calf bands and whose distal ends are the proximal part of the ankle joint mechanism. The shoe or foot attachment completes the mechanical ankle and anchors the orthosis distally. Primarily three types of shoe attachment devices have been used: stirrups, calipers, or shoe inserts.
Stirrups involve usually a solid, steel stirrup that is riveted directly to the sole of the shoe under the anterior section of the heel. The stirrup surrounds the heel and has a member going underneath the heel attached to it with fasteners.
A caliper involves a round tube placed in the heel of the shoe that receives the caliper for attachment. The caliper allows for interchangeability of shoes compared to the stirrups that are riveted. The draw-back of this design is that the pivot of the mechanical joint is typically at the level of the shoe heel.
With a shoe insert, a stirrup-like arrangement is essentially incorporated into the interior of the shoe and is shaped to contour to the patient's foot that fits into the shoe. Considerable time and skill are required to fabricate a proper insert of this type. Further, a larger shoe is typically required to accommodate the insert.
Between the shoe attachments and the metal upright posts is the ankle joint mechanism. These joint mechanisms are frequently single-axis joints that control mediolateral motion by stopping or blocking it and dorsiflexion and plantar flexion by means by stops or assists. The stops limit the movement and may be placed as a plantar-flexion (posterior) stop and/or a dorsiflexion (anterior) stop. The assists are usually springs that aid motion. With a dorsiflexion assist (anterior), the spring is compressed after heel strikes which helps to control plantar flexion.
Concerning the uprights or posts in the calf bands, historically the most frequently used have been the tube post design, but a single bar brace can be used in cases of relatively mild dorsiflexion weakness. Further, with molded plastic designs, a molded calf shell may be desirable that surrounds a substantial portion of the posterior portion of a patient's lower leg.
While developed systems have provided assistance to patients, there are a number of shortcomings. For example, conventional designs of AFOs do not allow for use with a patient's existing shoes and do not allow for easy removal without including bulky attachments.